This invention relates generally to medical implants, and more particularly to methods and apparatus for removing medical implants.
Medical implants, such as knee, hip, shoulder, and spine orthopedic replacement joints and other joints and implants typically comprise one or more bone-implantable elements connected to one or more articulating elements. Other implants such as intramedullary rods, screws and plates also have bone integration features. The bone-implantable elements are implanted into the bones of the joint, and the articulating elements, when present, bear against each other to transfer loads between the bones while permitting appropriate movement (e.g. ball-and-socket, hinge, and/or sliding action).
For example, FIG. 1 illustrates a typical implant 10 in a human body. More specifically, the implant 10 is a hip endoprosthesis comprising a cup 12 implanted into the acetabulum 14 of a pelvis 16 and carrying a hemispherical liner 18, and a stem 20 implanted into the canal 22 of the femur 24, from which the native femoral head has been removed. The stem 20 carries a ball 26 which articulates against the liner 18.
Post-implantation, a bond interface 28 is present between the stem 20 and the surrounding bone “B”. Depending on the specific implantation method, the bond interface 28 could be metal-to-bone, metal-to-cement-to bone, metal-to-oxidation layer-to-bone (especially when titanium is the implant substrate), or metal-to-coating-to-bone.
For various reasons such as wear, damage, or a desire to substitute a newer implant design, it is often desirable to remove or extract an implant. However, the pull-out force is significant because the bond interface 28 extends over a large surface area. In the prior art, extraction often requires brute-force mechanical extraction tools, such as the slide hammer 30 shown in FIG. 2, optionally combined with cutting or chiseling cement and/or bone away from the implant perimeter. This method consumes significant amounts of valuable time of the surgeon and hospital. It also subjects the patient (who is often elderly) to long times under anesthesia with attendant risk, and it can cause significant trauma to the bone and surrounding structures.
Accordingly, there is a need for an apparatus and method to extract implants quickly without excessive effort or damage.